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271.
Daniel A. Griffith Michael P. O'Neill Wende A. O'Neill Lloyd A. Leifer Rodric G. Mooney 《The Professional geographer》1986,38(3):263-270
Considerable attention has been devoted to shape analysis in geography with few fruitful results. We ask whether or not shape analysis is worth pursuing, referring to papers by Griffith and Lo. The methodology utilizes a two-step procedure. First, Lo's analysis is reconstructed to include indices reported in Griffith. Second, findings from the investigations are compared. Similar results are obtained from both studies, but the failure to extract any one-to-one correspondence between a shape and its associated index value(s) continues to cast doubt on the utility for subsequent studies. 相似文献
272.
273.
J. Ulrych J. Peek J. te
pnkov-Svobodova P. Bosk F.E. Lloyd V. von Seckendorff M. Lang J.K. Novk 《Chemie der Erde / Geochemistry》2006,66(1):37-56
Extensive Permo-Carboniferous volcanism has been documented from the Bohemian Massif. The late Carboniferous volcanic episode started at the Duckmantian–Bolsovian boundary and continued intermittently until Westphalian D to Stephanian B producing mainly felsic and more rarely mafic volcanics in the Central Bohemian and the Sudetic basins. During the early Permian volcanic episode, after the intra-Stephanian hiatus, additional large volumes of felsic and mafic volcanics were extruded in the Sudetic basins. The volcanics of both episodes range from entirely subalkaline (calc-alkaline to tholeiitic) of convergent plate margin-like type to transitional and alkaline of within-plate character. A possible common magma could not be identified among the Carboniferous and Permian primitive magmas, but a common geochemical signature (enrichment in Th, U, REE and depletion in Nb, Sr, P, Ti) in the volcanic series of both episodes was recognized. On the other hand, volcanics of both episodes differ in intensities of Nb, Sr and P depletion and also, in part, in their isotope signatures. High 87Sr/86Sr (0.707–0.710) and low εNd (−6.0 to −6.1) are characteristic of the Carboniferous mafic volcanics, whereas low 87Sr/86Sr (0.705–0.708) and higher εNd ranging from −2.7 to −3.4 are typical of the Permian volcanics. Felsic volcanics of both episodes vary substantially in 87Sr/86Sr (0.705–0.762) and εNd (−0.9 to −5.1). Different depths of magma source or heterogeneity of the Carboniferous and Permian mantle can be inferred from variation in some characteristic elements of the geochemical signature for volcanics in some basins. The Sr–Nd isotopic data with negative εNd values confirm a significant crustal component in the volcanic rocks that may have been inherited from the upper mantle source and/or from assimilation of older crust during magmatic underplating and ascending of primary basic magma. Two different types of primary magma development and formation of a bimodal volcanic series have been recognized: (i) creation of a unique magma by assimilation fractional crystallization processes within shallow-level reservoirs (type Intra-Sudetic Basin) and (ii) generation and mixing of independent mafic and felsic magmas, the latter by partial melting of upper crustal material in a high-level chamber (type Krkonoše Piedmont Basin). A similar origin for the Permo-Carboniferous volcanics of the Bohemian Massif is obvious, however, their geochemical peculiarities in individual basins indicate evolution in separate crustal magma chambers. 相似文献
274.
Laboratory experimental results show that adsorption can be an important mechanism in taking up heavy metals contained in
groundwaters in the sandstones. The adsorption can be described in terms of Freundlich isotherms and can be simply modeled
mathematically.
The adsorption function has been integrated into a mass balance equation, and tested using a laboratory sand tank model and
in a small field study. The results show that the transport-adsorption models are not easily applied in the field because
of hydrogeological complications. 相似文献
275.
Dr. Adrian J. Lloyd 《International Journal of Earth Sciences》1964,53(2):551-580
Sonmartel forms part of the anticlinal Cornu-Foulets Chain of the Neuchâtel High Jura. The strata exposed in the district include much of the Malm (Argovien to Purbeckien), the Lower Cretaceous (Berriasien to Hauterivien) and some Tertiary rocks (Siderolithique, Helvetian Miocene). An outline account is given of the Mesozoic formations, the distribution of marker bands being shown on the map (Pl. 1). The structure of the area is discussed in terms of its constituent parts. The folding is concentric but due to erosion-breaching following the earliest movements, subsequent deformation of the Pre- and Post-Kimeridgien rocks differed. The former are gently diapiric, while the folding of the latter is, in part, a gravity effect. Faults normal to the fold axes are present everywhere. They originated as tension cracks but later permitted transcurrent movements. Tear faults are best developed in regions where the trend of the fold axes changes. Thrusts are restricted to the Grand Sonmartel area. The joint systems are thought to result from stresses due to bed-over-bed sliding during the folding. The different types of deformation combine to produce a rhomboidal pattern of dissected cross-folds. Each of these strain-phenomena show that the region has been subjected to stresses of two different orientations, with a third also affecting the vicinity of Grand Sonmartel. These owe their origins to relative movements of basement blocks beneath the area — thrusting during the Post-Stampian phase, the thrusts re-activated as sinistral shears during the Post-Pontian phases when they were joined by conjugate dextral shears. On this basis the Alpine Push theory for the origin of the Folded Jura must be rejected. The Wegmann hypothesis of basement shears accounts best for the structures observed. 相似文献
276.
Ryan North Lloyd T. White Mitchell Nancarrow Anthony Dosseto Dominique Tanner 《Geostandards and Geoanalytical Research》2023,47(1):125-142
Zircon geochemistry can vary over micrometre scales; therefore, natural reference materials need to be well characterised before being used to calculate trace element mass fractions in unmeasured samples. Moreover, reference material homogeneity needs to be ensured with the accelerating rate of geoanalytical developments to map mineral chemistry at increasingly finer scales. Here, we investigate trace element zoning in four widely used zircon reference materials: 91500, Mud Tank, Temora and Plešovice, as well as zircon crystals from the Mount Dromedary/Gulaga Igneous Complex, Australia. Sub-micrometre resolution focused ion beam scanning electron microscope (FIB-SEM) based time-of-flight secondary ion mass spectrometry (ToF-SIMS) and 5 μm resolution LA-ICP-MS mapping show that trace elements are zoned in all reference materials, though 91500 exhibited the least zonation. We demonstrate that FIB-SEM-based ToF-SIMS can rapidly resolve variations in trace elements (e.g., U, Th, Sc, Y, Gd, Dy, Yb and Li) at sensitivities down to the μg g-1 level with a spatial resolution of 195 nm for areas 100 × 85 μm to 959 × 828 μm. Zircon 91500 is recommended for future quantitative analyses provided that (1) the spatial distribution of elements is imaged before analysis of unknown samples and (2) it is used in conjunction with a doped glass as the primary reference material. 相似文献
277.
Louise Best Alexander R. Simms Martin Brader Jerry Lloyd Juliet Sefton Ian Shennan 《第四纪科学杂志》2022,37(1):59-70
New relative sea-level (RSL) data constrain the timing and magnitude of RSL changes in the southern Isle of Skye following the Last Glacial Maximum (LGM). We identify a marine limit at ~23 m OD, indicating RSL ~20 m above present c. 15.1 ka. Isolation basin data, supported by terrestrial and marine limiting dates, record an RSL fall to 11.59 m above present by c. 14.2 ka. This RSL fall occurs across the time of global Meltwater Pulse 1A, supporting recent research on the sources of ice melting. Our new data also help to resolve some of the chronological issues within the existing Isle of Skye RSL record and provide details of the sub-Arctic marine environment associated with the transition into Devensian Lateglacial climate at c. 14.5 k cal a bp , and the timing of changes in response to the Loch Lomond Stadial climate. Glacio-isostatic adjustment (GIA) model predictions of RSL deviate from the RSL constraints and reflect uncertainties in local and global ice models used within the GIA models. An empirical RSL curve provides a target for future research. 相似文献